The electrical power network is composed of various sections and components, including numerous transmission and distribution networks, each operating at different voltage levels. Each part of the power network must be protected against electrical faults and consequently short circuits that could cause a collapse of the network, serious and expensive equipment damage, and personal injury. Protective devices, including circuit breakers and reclosers controlled by relays are located throughout the various parts of the power network to locate and attempt to isolate the faults as they occur.
One particular portion of the power network often is referred to as the “loop.” The loop refers to the final portion of the electrical power system that connects the consumers to the distribution system. Often, protection schemes referred to as “loop control” are directed to this portion of the electrical network. To date, loop control has been accomplished on overhead power systems using reclosers that are located beside the electrical transformers located atop electrical poles. Reclosers break the larger portions of the power network into smaller sections by automatically isolating faults and restoring power to the unfaulted sections. For example, if lightning created a fault on the power system, a recloser or group of reclosers will open for a preprogrammed time before reclosing automatically (i.e., auto-reclose) once the fault is cleared, so as to restore power to the faulted section.
One drawback of using reclosers to clear faults is that often power is reclosed into the fault. In particular, because reclosers automatically close after a predetermined period of time, without knowing whether the fault has been cleared, current may be restored to the faulted section even though the fault remains. Providing current to the faulted section, often referred to as “banging the cable,” causes damage to the cable by promoting a dangerous overcurrent situation. Over time, the insulation and conductivity of the “banged” cable may be diminished to the point that the cable is incapable of carrying its rated current, and must therefore be replaced.
In an overhead environment, where the damaged loop cables are readily accessible, “banging the cable” (and thus having to replace the cable over time) is considered a worthwhile tradeoff to more expensive fault-protecting alternatives. However, in an underground environment, where the damaged loop cables are buried many feet below the ground such that replacing a damaged cable is an expensive undertaking, banging the cable is not a viable alternative. Accordingly, for underground loop systems, which recently have become more widely used than their overhead counterparts, automatic loop control (e.g., using reclosers) is not a viable option. Instead, to date, underground loop systems have tended to use non-fault-interrupting devices, called load break switches.
A load break-switching device is a manually operated device capable of interrupting supply on a distribution network while load current is flowing. A load break device, however, is not designed to interrupt fault currents, but to simply redirect a power source to restore supply to customers. As a result, a load break system requires a line crew to go into the field, locate and clear the fault by manually opening the load break switch. Alternatively, underground loop systems may employ sophisticated point-to-point communication systems that permit a faulted section of the loop to communicate fault-based data to all of the un-faulted section. However, these point-to-point communication systems are complicated and expensive, especially in the underground environment.
Therefore, a need exists to provide efficient and cost-effective loop control for electrical distribution systems.